Nearly all locations within the United States and Canada are now served by “911” emergency telephone service, and many other countries have similar services. In the 911 system, calls to the telephone number 911 are specially routed to a public safety answering point (PSAP), where a specially-trained dispatcher can assess the nature of the emergency, offer assistance, summon emergency services or law enforcement personnel to the source of the call, or provide other services. Many PSAPs are interconnected to allow routing calls and other information between them. The 911 service facilitates rapid response by the appropriate authorities in cases of emergency.
In order to maximize the effectiveness of 911 service, special rules apply to the handling of many 911 calls. For example, in the wireline Enhanced 911 system, provision must be made for the dispatcher to call back to the telephone that placed a 911 call, in the event a call is interrupted for any reason, for example mistakenly by a distraught or injured caller. In conventional wireline systems, a 911 dispatcher knows the location of the caller, because the location of the telephone from which the call is made is known through caller ID or similar services.
The handling of 911 calls is complicated by the increasing use of mobile telephones. Because the location of a mobile telephone is not fixed, the 911 dispatcher may have an increased need for verbal communication with the caller in order to learn the location of the emergency, so that emergency services or law enforcement personnel can be sent to the scene. Location services for mobile phones determine and route location information to the PSAP to facilitate dispatch of emergency responders to the caller.